Numerical simulation of two-phase steam ejector applied in novel loop heat pipe

doi:10.11949/0438-1157.20231132

Abstract

Abstract:

As an efficient passive phase-change heat transfer device, loop heat pipe (LHP) is widely used in industrial fields such as heat dissipation of high-heat-flux electronic devices. Based on previous research, flat-plate LHP coupled with a micro two-phase steam ejector can significantly improve heat transfer performance. However, the internal flow and heat transfer mechanisms of micro two-phase steam ejector were still unclear, making it difficult to perform forward design and theoretical modeling of novel LHP. The effects of steam-water parameters and mixing chamber structure on the performance and internal flow field distribution of the two-phase steam ejector were studied through numerical simulation. The results show that a condensation shock wave exists downstream of the throat. As back pressure increases, the position gradually moves towards the throat. The intensity of condensation shock wave is positively correlated with back pressure, steam mass flow rate and mixing chamber length, while negatively correlated with water temperature. The maximum back pressure of the ejector is in the range of 40—125 kPa and positively correlated with heat load and water temperature, while negatively correlated with mixing chamber length. Through extensive simulation, the influence of water temperature and mixing chamber length on the operating state and pressure ratio of two-phase steam ejector under design power were obtained.

Key words: loop heat pipe, ejector, heat transfer, two-phase flow, condensation, shock wave, numerical simulation

摘要：

环路热管是一种高效被动式相变传热装置，广泛应用于高热流电子器件散热等领域。前期研究发现将小型两相引射器与平板式环路热管耦合，可大幅提高传热性能。然而，小型两相引射器内部流动及传热机理尚不清晰，难以对新型环路热管进行正向设计与理论建模。通过数值模拟研究了汽水参数和混合腔结构对两相引射器性能及内部流场分布的影响。结果表明，喉部下游存在凝结激波，随着背压增加，其位置逐渐向喉部移动；其强度与背压、蒸汽产量、混合腔长度呈正相关，与水温呈负相关。引射器最大工作背压在40~125 kPa，与蒸汽产量和水温呈正相关，与混合腔长度呈负相关。通过大量模拟，得到了设计功率下水温和混合腔长度对引射器工作模式和压比的影响规律。

关键词: 环路热管, 引射器, 传热, 两相流, 凝结, 激波, 数值模拟

CLC Number:

TK 124

Yao ZHOU, Xiaoping YANG, Yicheng NI, Jiping LIU, Jinjia WEI, Junjie YAN. Numerical simulation of two-phase steam ejector applied in novel loop heat pipe[J]. CIESC Journal, 2024, 75(1): 268-278.

周尧, 杨小平, 倪一程, 刘继平, 魏进家, 严俊杰. 应用于新型环路热管的两相引射器数值模拟[J]. 化工学报, 2024, 75(1): 268-278.

Figures/Tables 20

Fig.1 Schematic diagram of novel LHP system coupled with two-phase steam ejector1—evaporator; 2—vapor line; 3—two-phase steam ejector; 4—liquid line Ⅰ; 5—cooler Ⅰ; 6—liquid line Ⅱ; 7—cooler Ⅱ

Fig.2 Schematic diagram of two-phase steam ejector sturcture1—steam nozzle; 2—water nozzle; 3—mixing chamber; 4—throat; 5—diffuser

Table 1 Geometry dimensions and boundary conditions of two-phase steam ejector

几何参数及边界条件	结构1	结构2	结构3	结构4
蒸汽喷嘴喉部直径, d_st/mm	1.24	1.24	1.24	1.24
蒸汽喷嘴出口直径, d_so/mm	1.5	1.5	1.5	1.5
混合腔入口直径, d_mi/mm	2.8	2.8	2.8	2.8
喉部直径, d_m/mm	1.8	1.8	1.8	1.8
混合腔长度, l_m/mm	13	11	9	7
喉部长度, l_t/mm	2	2	2	2
扩散段出口直径, d_d/mm	4	4	4	4
蒸汽喷嘴壁面厚度, δ/mm	0.25	0.25	0.25	0.25
蒸汽入口压力, p_s/kPa	60~167	149	149	149
蒸汽喷嘴喉部质量流率, G_s/(kg/(m²·s))	95~257	232	232	232
蒸汽入口温度, T_s/℃	85.9~115	111	111	111
水喷嘴出口质量流率, G_w/(kg/(m²·s))	830~2238	2020	2020	2020
水喷嘴入口温度, T_w/℃	5~55	5~55	2~55	2~55
出口背压, p_b/kPa	40~129	79~114	89~113	91~105

Fig.3 Schematic diagram of interphase heat/mass transfer model

Fig.4 Schematic diagram of structure mesh solution of two-phase ejector

Fig.5 Validation of mesh independence

Table 2 Comparison of steady-state data between experiment［16］ and numerical simulation in two-phase ejector

加热功率Q/W	蒸发热量Q_evap/W	加热性能ΔT			蒸汽入口压力p_s
加热功率Q/W	蒸发热量Q_evap/W	实验值/℃	模拟值/℃	相对误差/%	实验值/kPa	模拟值/ kPa	相对误差/%
450	343	31.0	30.1	0.32	69.9	71.3	-2.0
550	430	37.7	35.7	0.64	87.7	89.5	-2.1

Fig.6 Comparison of pressure and temperature distribution between experiment[36] and numerical simulation

Fig.7 Contours of steam void fraction and axial pressure at different discharge pressure

Fig.8 Contours of steam void fraction and axial pressure at maximum discharge pressure and different steam mass flow rates

Fig.9 Contours of steam void fraction and axial pressure at maximum discharge pressure and different water temperature

Fig.10 Contours of steam void fraction and axial pressure at maximum discharge pressure and different mixing chamber

Fig.11 Schematic diagram of steam-water mixing layer and inner/outer border of steam plume

Fig.12 Pressure difference and pressure ratio between two sides of condensation shockwave at different back pressure

Fig.13 Pressure difference and pressure ratio between two sides of condensation shockwave at maximum discharge pressure and different steam mass flow rates

Fig.14 Pressure difference and pressure ratio between two sides of condensation shockwave at maximum discharge pressure and different water temperature

Fig.15 Pressure difference and pressure ratio between two sides of condensation shockwave at maximum discharge pressure and different mixing chambers

Fig.16 Operation mode with water temperature and mixing chamber length of two-phase ejector

Fig.17 Steam pressure ratio with water temperature and mixing chamber length

Fig.18 Water pressure ratio with water temperature and mixing chamber length

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